TITLE:
The Effects of Surface Water Velocity on Hyporheic Interchange
AUTHORS:
Timothy Sickbert, Eric W. Peterson
KEYWORDS:
Hyporheic Zone; Bernoulli Equation; Venturi Effect; Geomorphology; Fluvial; Groundwater/Surface Water Interaction; Streamflow
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.6 No.4,
March
28,
2014
ABSTRACT:
When
evaluating hyporheic exchange in a flowing stream, it is inappropriate to
directly compare stream stage with subsurface hydraulic head (h) to determine direction and magnitude
of the gradient between the stream and the subsurface. In the case of moving
water, it is invalid to ignore velocity and to assume that stage equals the net
downward pressure on the streambed. The
Bernoulli equation describes the distribution of energy within flowing fluids
and implies that net pressure decreases as a function of velocity, i.e., the Venturi Effect, which
sufficiently reduces the pressure on the streambed to create the appearance of
a downward gradient when in fact the gradient may be upward with stream flow
drawing water from the subsurface to the surface. A field study correlating the
difference between subsurface head and stream stage in a low-gradient stream
indicates that the effect is present and significant: shallow subsurface head
increases less quickly than stage while deeper subsurface head increases more
quickly. These results can substantially improve conceptual models and
simulations of hyporheic flow.